Joint Dip Angle Research Articles

Anisotropic mechanical characteristics and energy evolution of artificial columnar jointed rock masses subjected to multi-level cyclic loading

Columnar jointed rock masses (CJRM) are natural geological structures with regular and irregular polygons. Because of the joints throughout, the rock mass mechanical properties are severely degraded. This study focused on the effect of joint dip angle, fatigue effect, and stress level on the anisotropic strength, deformation behavior, energy evolution characteristics, and failure mode of CJRM specimens. Triaxial compression and multi-level cyclic loading tests were performed on artificial CJRM specimens with a similar geological structure under a 7 MPa confining pressure. Energy dispersive spectroscopy (EDS) tests were performed on the hexagonal prism and joint structure to investigate the failure mechanism of the CJRM specimens. The experimental results show that the relationship between the characteristic stress and the joint dip angle is a typical U-shaped pattern. The anisotropy of characteristic stresses decreases gradually under triaxial compression. The fatigue effect increases peak strength's anisotropy and decreases residual strength's anisotropy. The plastic strain and strain energy depend on stress level, fatigue effect, and joint dip angle. Three failure modes were observed. Disintegration and fracture of hexagonal prisms, and joint cracking result in the failure of CJRM specimens. Overall, the fatigue effect increases the number and distribution of cracks in CJRM specimens.

Damage Constitutive and Failure Prediction of Artificial Single-Joint Sandstone Based on Acoustic Emission

The effect law of deformation and failure of a jointed rock mass is essential for underground engineering safety and stability evaluation. In order to study the evolution mechanism and precursory characteristics of instability and failure of jointed rock masses, uniaxial compression and acoustic emission (AE) tests are conducted on sandstones with different joint dip angles. To simulate the mechanical behavior of the rock, a jointed rock mass damage constitutive model with AE characteristic parameters is created based on damage mechanics theory and taking into account the effect of rock mass structure and load coupling. To quantify the mechanism of rock instability, a cusp catastrophe model with AE characteristic parameters is created based on catastrophe theory. The results indicate that when the joint dip angle increases from 0° to 90°, the failure mechanism of sandstone shifts from tensile to shear, with 45° being the critical failure mode. Sandstone's compressive strength reduces initially and subsequently increases, resulting in a U-shaped distribution. The developed damage constitutive model's theoretical curve closely matches the test curve, indicating that the model can reasonably describe the damage evolution of sandstone. The cusp catastrophe model has a high forecast accuracy, and when combined with the damage constitutive model, the prediction accuracy can be increased further. The research results can provide theoretical guidance for the safety and stability evaluation of underground engineering.

Does joint structure promote the development of gully erosion?

Gully erosion is a growing environmental problem around the world, and limits ecological and economic development. Collapse gullies in the granite mountainous region of southern China are unique gully erosion occurrences known locally as Benggang, and its erosion gully is made up of a main gully and multiple branch gullies that form a runoff and sediment drainage channel system. Joint structure is the product of geological movement. To investigate the internal relationship between the morphological development of gullies and joint structure, we measured and recorded morphological parameters, including the area, strike, quantity and depth of gullies and the strike, dip angle, density and wall distance of joints, in four typical granite gully erosion regions. Our findings are as follows: (i) as a unique gully erosion phenomenon, the development intensity of Benggang increases from north to south, and erosion becomes more severe; (ii) the average joint area densities range from 19.41/m2 to 21.85/m2, while the average joint ratios range from 7.40 to 10.32. Overall, joint development gradually increases from north to south, characterized by a high density, clear dominant direction, high dip angle (mostly ranging from 50 to 80°), and high inheritance and considerable influence on the resulting soil structure; (iii) correlation analysis reveals that the erosion gully development direction and dominant joint strike basically coincide, and are significantly positively correlated (P < 0.001); (iv) the average depths of the main gullies in Tongcheng (TC), Ganxian (GX), Changting (CT) and Wuhua (WH) along the dominant joint strike are greater than those along other joint strikes, and deeper main gully depths correspond to more high-angle joints along the same strike. The dip angles of joints along the strike of the branch gully with the maximum depth are greater than 60°, and some branch gullies follow the dominant joint strike. This study concludes that the joint strike controls the development direction of erosion gully and that the depth of erosion gully is greater than that of other strikes in the dominant strike direction where the number of joints is concentrated. Joints aggravate soil erosion and promote the development of gully erosion.

Research on Zonal Disintegration Characteristics and Failure Mechanisms of Deep Tunnel in Jointed Rock Mass with Strength Reduction Method

To understand the fracture features of zonal disintegration and reveal the failure mechanisms of circle tunnels excavated in deep jointed rock masses, a series of three-dimensional heterogeneous models considering varying joint dip angles are established. The strength reduction method is embedded in the RFPA method to achieve the gradual fracture process, macro failure mode and safety factor, and to reproduce the characteristic fracture phenomenon of deep rock masses, i.e., zonal disintegration. The mechanical mechanisms and acoustic emission energy of surrounding rocks during the different stages of the whole formation process of zonal disintegration affected by different-dip-angle joints and randomly distributed joints are further discussed. The results demonstrate that the zonal disintegration process is induced by the stress redistribution, which is significantly different from the formation mechanism of traditional surrounding rock loose zone; the dip angle of joint set has a great influence on the stress buildup, stress shadow and stress transfer as well as the failure mode of surrounding rock mass; the existence of parallel and random joints lead the newly formed cracks near the tunnel surface to developing along their strikes; the random joints make the zonal disintegration pattern much more complex and affected by the regional joint composition. These will greatly improve our understanding of the zonal disintegration in deep engineering.

Strength criterion of rock mass considering the damage and effect of joint dip angle

It is highly significant to theoretically assess the effect, under load, of initial stress and structure on the mass damage of rock mass. In this reported study, first a multi-factor coupling damage constitutive model under the action of joint-load was established by fully considering the non-uniformity, anisotropy and initial structure of a rock mass based on the Weibull distribution and D-P criterion. The relationship between the damage evolution and joint angle in the rock mass was elaborated. Then, a jointed rock mass strength criterion was built in line with the D–P criterion and the limit state of rock mass failure by the method of multivariate function total differential as based on the constitutive model. The results showed that the established constitutive model was in good agreement with the test results, which accurately reflected the damage characteristics of jointed rock mass during the entire loading process. The initial damage value of the rock mass increased with increasing joint dip angles, and the damage evolution of the jointed rock mass could be divided into the initial, stable, accelerated and failure damage stages. Comparing the results of this approach with other methods it was found that the strength criterion better reflected the effects of minimum principal stress σ3, volume stress σm, shear stress J21/2 and joint dip angle β on rock mass strength than other existing strength criteria, which showed that the proposed method offered important guiding principles for the engineering practice.

Study on Dynamic Response of Rock Slope With Inverse Non-Persistent Joints Under Earthquake

Based on the two-dimensional discrete element software UDEC, this article studied the dynamic response laws of rock slopes with inverse nonpersistent joints by the combination of different dip angles and spacing of joint and length of rock bridge under earthquake. The results showed that the existence of the joint surface had a significant impact on the dynamic response of the slope. When the dip angle of inverse nonpersistent joint increases or the joint spacing decreases, the PGA amplification factor of each monitoring point on the slope surface increases, and the influence range is mainly concentrated in the middle of the slope surface to the slope shoulder. Along the horizontal direction of the slope, closer to the shoulder of the slope, the PGA amplification factor increases with the increase of the joint dip angle and the decrease of rock bridge length and joint spacing; along the vertical direction, the PGA amplification coefficient curve increases first, then decreases, and then increases with the change of elevation, and the dynamic response of slope reacts the most violent where the joints are densely developed.

Numerical Modeling on Dynamic Characteristics of Jointed Rock Masses Subjected to Repetitive Impact Loading

A discrete element method code was used to investigate the damage characteristics of jointed rock masses under repetitive impact loading. The Flat-Joint Contact Model (FJCM) in the two-dimensional particle flow code (PFC2D) was used to calibrate the microparameters that control the macroscopic behavior of the rock. The relationship between macro- and microparameters by a series of uniaxial direct tension and compression numerical tests based on an orthogonal experimental design method was obtained to calibrate the microparameters accurately. Then, the Synthetic Rock Mass (SRM) method that incorporates joints into the calibrated particle model was used to construct large-scale jointed rock mass specimens, and the repetitive drop hammer impact numerical tests on SRM specimens with different numbers of horizontal joints and dip angle joints were carried out to study the damage evolution, stress wave propagation, and energy dissipation characteristics. The results show that the greater the number of joints, the greater the number of cracks generated, the greater the degree of damage, and the more energy dissipated for rock masses with horizontal joints. The greater the dip angle of joints, the less the number of cracks generated, the less the degree of damage, and the less energy dissipated for rock masses with different dip angles of joints. The impact-induced stress waves will be reflected when they encounter preexisting joints in the process of propagation. When the reflected stress waves meet with subsequent stress waves, the stress waves will change from compressional waves to tensile waves, producing tensile damage inside rock masses.

Anisotropic mechanical behaviour of columnar jointed rock masses subjected to cyclic loading: An experimental investigation

In order to investigate the anisotropic mechanical behaviour of the columnar jointed rock masses (CJRM) under cyclic loading, triaxial cyclic loading-unloading tests are conducted on artificial CJRM specimens with a geological structure similar to the actual CJRM under the confining pressures of 5 MPa. In this work, particular attention is paid on the influence of joint dip angles on the anisotropic deformation behaviour , strength, mechanical properties, and failure modes of the CJRM. The experimental results show that the relationship between characteristic stress thresholds and joint dip angles is exhibited as a typical U-shape. Crack unstable growth ( σ cu ) and crack damage ( σ cd ) stress thresholds are more anisotropic than the crack stable growth stress threshold ( σ cs ), peak stress ( σ p ) and residual stress ( σ r ). The CJRM anisotropy mechanical parameters induced by stress gradually increases. Three main failure modes are observed throughout the loading process with respect to the joint dip angles. The results presented in this paper are significant for understanding the mechanical behavior of anisotropy in rock engineering.

Experimental and Numerical Investigation of Failure Characteristics and Mechanism of Granites with Different Joint Angles

The uniaxial compression tests were conducted on granite samples with different joint dip angles to more favorably explore the influences of the nonconsecutive joint on mechanical properties and deformation characteristics of the rock mass. The stress-strain curves, deformation and strength characteristics, and energy evolution process of the samples were analyzed. Numerical simulation using particle flow code (PFC) is employed to study the crack propagation process. The mode of jointed and fractured rock was investigated. The research results showed a significant reduction in both the peak strength and elastic modulus of jointed samples compared with intact ones: the peak strength and elastic modulus drop to the minimum at the joint dip angle of about 45°, especially for the peak strength, which takes up about 55% of the intact samples. The fractured samples’ total energy, elastic strain energy, and dissipated energy during the uniaxial compression drop significantly relative to intact samples. The proportion of the fracture modes varies with different joint dip angles, in which the ratio of shear cracks grows at first and then declines, with the highest balance at the dip angle of 45°. The damage stress’s sensitivity to the dip angle change is greater than that of the peak stress, with reduction amplitude more extensive than the latter.

The Effect of Joint Damage on a Coal Wall and the Influence of Joints on the Abutment Pressure on a Fully Mechanised Working Face with Large Mining Height

Coal wall spalling is regarded as a key technical problem influencing safe and efficient mining of large-mining-height working faces while the distribution of abutment pressure within the limit equilibrium zone (LEZ) influences coal wall spalling within a large-mining-height working face. This research attempted to explore the distribution characteristics of abutment pressure within the LEZ in a large-mining-height working face. For this purpose, the influences of the orientation of joints on mechanical characteristics of coal with joints and on the distribution of abutment pressure within the LEZ in the large-mining-height working face were analysed by theoretical analysis and numerical simulation. Research results show that the damage variable of coal with joints first rises, then decreases, and finally increases with increasing dip angle of the joints; as the azimuth of the joints increases, the damage variable first declines, then increases; the damage variable gradually declines with increasing joint spacing; an increase in the dip angle of joints corresponds to first reduction, then growth, and a final decrease of the abutment pressure at the same position in front of the coal walls; on certain conditions, the abutment pressure at the same position within the LEZ first rises, then declines as the azimuth of joints increases; with the growth of the joint spacing, the abutment pressure at the same position within the LEZ rises. The dip angle and azimuth of joints marginally affect the abutment pressure within the LEZ.

Influence of Joint Dip Angle on Dynamic Mechanical Properties and Crack Propagation Law of Rock-like Materials

The main objective of this study is to investigate the dynamic mechanical properties and crack propagation law of rock-like materials with different joint dip angles. The precast cement mortar specimens are impacted by split Hopkinson pressure bar (SHPB). The meso damage of the specimens before and after impact is detected by nuclear magnetic resonance system (NMR), and the crack propagation path is extracted. The influence of joint dip angles on dynamic response characteristics of rock-like materials is analyzed from the aspects of dynamic compressive strength, meso damage and crack propagation path. The analysis indicates that joints make the internal stress distribution of rock-like materials uneven, resulting in the weakening of the dynamic compressive strength of rock-like materials. At the same time, joint characteristics affect the weakening degree of the dynamic compressive strength of rock-like materials. With the increase of joint dip angle, the weakening degree of dynamic compressive strength of rock like materials first increases and then decreases. The relationship between the damage degree and the dynamic compressive strength of rock-like materials is approximately negative linear. With the increase of joint dip angle, the damage degree changes in an inverted “U” shape. Tensile stress or the combination of tensile stress and shear stress leads to the initiation and propagation of cracks. The intact specimens, the specimens with joint dip angle of 0°, and the specimens with joint dip angle of 90° develop axial tensile cracks. The specimens with joint dip angles of 15°-75° develop tensile cracks and shear cracks at the joint tips.

Failure in rock with intersecting rough joints under uniaxial compression

Uniaxial compressive tests were performed on Y-jointed granite specimens to explore how intersecting rough joints affect the strength, failure mode, and precursory damage characteristics of the jointed rock mass. The mechanical properties, joint dip angles, and joint roughness of the specimens were measured prior to the tests, then the loading stress, surface displacement fields, acoustic emission (AE) signals, and failure modes were recorded during the loading process. As the uniaxial compressive strength (σc) of the specimens increased, three different failure modes appeared: shear failure along the persistent joint with rock wedge falling, compressive failure with rock wedge ejection, and overall crushing accompanied with rock fragment splashing, the σc thresholds of the three failure modes are about 50 MPa and 90 MPa, respectively. The deformability of the specimens weakened gradually as σc increased. AE events spread from the joint surface to the interior of the rock block until final failure. For specimens that failed in shear mode, multiple sudden stress drops along with sharp displacement increases occurred during the tests but no entire failure occurred. Other specimens tended to present one eventual unstable failure. When the peak shear strength of the non-persistent joint was higher than or near to that of the persistent joint, the σc of a given Y-jointed specimen was mainly determined by the persistent joint. Otherwise, it was simultaneously controlled by the two joints. Both the joint dip angle and joint roughness were found to significantly influence the σc of the specimens. Each stress drop was accompanied by significant AE signal variations, though the AE indicators are difficult to effectively utilize for early warning of specimen failure.

Effect of structural planes on rockburst distribution: Case study of a deep tunnel in Southwest China

Rockburst is a type of dynamic failure and often causes considerable damage during the construction of underground engineering. Geological structures have been regarded as a crucial factor influencing rockburst distribution, and more related research is urgently needed. This paper presents microseismic monitoring information, characteristics of 151 rockbursts, and various structural planes collected in detail from a deep tunnel located in Southwest China. The results show that microseismic activity tends to increase when joints with large scale begin to appear and vanish. Rockburst risk always increases between the spandrels and around the intersection of two joint sets. The joint dip angle changes the rockburst risk. In the presence of one or two joint sets with a 70– 80° dip angle, rockbursts are more prone to occur. The conclusions can be interpreted with the discrete element method. When more joints are encountered, the total number of rockbursts may decrease, but the rockbursts are more likely to be strong or induce collapse, causing more damage. This research can improve the understanding of rockburst mechanisms and guide the choice of construction and support methods.

Study on Stability and Plastic Zone Distribution of Tunnel with Thin Carbonaceous Slate at Different Dip Angles

Carbonaceous slate is heterogeneous and anisotropic, which has a great influence on the stability of tunnel. In this paper, by means of laboratory test, field measurement, and numerical simulation, the surrounding rock stability and plastic zone distribution characteristics of the carbonaceous slate tunnel at different intersection angles are analyzed. First, combined with the Haibaluo tunnel project, Brazilian splitting and uniaxial compression tests of jointed carbonaceous slate are performed. The test results show that the tensile strength of carbonaceous slate is related to joint dip angle. When the joint angle is 0°, the tensile strength is the largest and decreases with the increase of the joint angle. The uniaxial strength of rock decreases first and then increases. Based on the discrete fracture network (DFN) technology, a calculation model is established. The calculation results show that the maximum displacement is 0.45 m, when the dip angle of the surrounding rock joint is 45°. The field measurement also shows that the dip angle of the surrounding rock joint has an important influence on the distribution of the plastic zone. When the joint dip angle is 45°, the plastic zone develops most strongly.

Numerical investigation of the influence of discontinuity orientations on fault permeability evolution and slip displacement

A pre-existing plane of weakness along the fault is comprised of a particular pattern of joints dipping at different orientations. The fault stress state, partially defined by the orientation of fault, determines the potential of slip failure and hence the evolution of fault permeability. Here the influence of fault orientation on permeability evolution was investigated by direct fluid injection inside fault with three different sets of fault orientations (45°, 60° and 110°), through the coupled hydromechanical (H-M) model TOUGHREACT-FLAC3D. The influence of joints pattern on slip tendency and magnitude of potential induced seismicity was also evaluated by comparing the resulted slip distance and timing. The simulation results revealed that decreasing the dip angle of the fault increases the corresponding slip tendency in the normal fault circumstance. Also, with changing joints dip angle associated with the fault, the tendency of the fault slip changes concurrently with the permeability evolution in a noticeable manner. Permeability enhancement after the onset of fault slip was observed with the three sets of fault angles, while the condition of 60° dipping angle resulted in highest enhancement. Joints pattern with a dip angle of 145° (very high dip) and 30° (very low dip) did not trigger a shear slip with seismic permeability enhancement. However, high dip and intermediate dip angles (135°, 50° and 70°) yielded high permeability in varying orders of magnitude. The large stress excitation and increasing permeability during shear deformation was noticeably high in intermediate joint dip angles but decreases as the angle increases.Article highlightsThe magnitude of injection-induced permeability enhancement is largely influenced by the fault and joint spatial orientations.With a slight change in the joint direction, there is an increasing possibility for fault to approach a different critical state of failure.Stress elevation at the point of failure is controlled by the orientations of fault/joint planes with respect to the direction of maximum principal stress.

Effects of the attitude of dominant joints on the mobility of translational landslides

Geological structures and ground undulation affect the mobility of translational landslides. Combining field investigation, back-analysis, and numerical simulation, we explore the role of dominant joint dip angle in controlling the mobility of translational landslides. First, the attitudes of the geological structures are revealed by aerial photography measurements. The pre-failure slope surface of the Wolong landslide, Southeastern Tibetan Plateau, is estimated from the contours of the adjacent stable hillslopes and the deposit bottom boundary. Then, to back-analyze cohesion and internal fraction angle of the landslide, we fit a maximum stable relief limit based on Culmann’s model to the upper envelope of 96 rock scars and 37 previously published landslides. Next, we design eight scenarios (S1–S8) for the simulation of landslide mobility, respectively, corresponding to the eight joint dip angles between 20° and 60°. The mobility index H/L increases with the dip angle β, as confirmed by the best-fit line H/L = 0.288 ln(β) − 0.698. The numerical results of the runout characteristics, velocity, and energy consumption of the simulated landslides in the eight scenarios indicate that (1) the momentum losses at slope break are closely related to the joint dip, apparent friction angle, and height of the mass center; (2) local undulations in substrate have an inapparent effect on mobility of large and long runout landslides; and (3) conventional mobility indexes need to be improved or modified when high mobile landslides encounter high obstacles at slope bottom, opposite hills, or mountains. This study will be useful for hazard evaluations of translational landslides in mountainous regions.

Dynamic mechanical properties of jointed soft rock samples subjected to cyclic triaxial loading: a FEM-DEM-based study

In order to investigate the fatigue behavior of jointed soft rock samples with different joint dip angles, cyclic triaxial tests under different stress amplitudes and confining pressures were numerically simulated using the combined finite-discrete element method (FEM-DEM). The dynamic strength and deformation rules were revealed, including the masing effect, the ratcheting effect, the volumetric strain properties and the failure modes influenced by joint dip angles. During the first hysteresis loop, the nonlinearity of the loading curve is much stronger than that in subsequent cycles, and the damage and deformation are almost the most, which demonstrates that the effect of stress history on soft jointed samples subjected to cyclic loading is great, especially the first loading cycle. When the applied static and dynamic maximum deviatoric stress are the same, the vertical compressive stress of the dynamic case is found to be lower than that of the static case, and the vertical tensile stress exists in some local position, which may be the reason why the cracks can increase and propagate gradually when the dynamic maximum stress is lower than the static strength.

Experimental Study on Shear Failure Characteristics of Jointed Rock Mass Based on Direct Shear Tests and Digital Image Correction Techniques

The instability of rock engineering is normally dominated by the shear failure of rock mass. The dip angle of discontinuous planes widely existing in rock mass is a key parameter affecting the shear strength and failure mode of jointed rock. This paper aims to investigate the influence of discontinuous joints on the shear failure of rock. Direct shear tests are carried out on rock-like specimens with discontinuous joints in different dip angles. During the shear tests, the strain field is monitored in real-time by digital image correction (DIC) technology. Experimental results show that the shear strength, shear strain evolution, and failure mode for the jointed specimens are affected by the dip angles of the discontinuous joints. The maximum shear strain of specimens with joint angles of 45° and 75° increases gradually with the increase of shear loading. The maximum shear strain for the specimens with joint angles of 0°, 15°, 30°, 60°, and 90° increases sharply after the shear load reaches 80% of the peak load. When the joint inclination angle is less than 45°, the crack begins to expand from the joint tip and is interconnected to form a penetrating fracture. When the joint dip angle is greater than 45°, the cracks initiate at the joint tip and then propagate at different paths resulting in multistage shearing and crushing failure.

Study on mechanical properties of 3D printed rock mass samples with photosensitive resin material

3D printing technology can provide an effective method for specimen preparation of rock mass, but the mechanical properties of 3D printed rock mass still need to be further studied. In this paper, uniaxial compression tests are carried out on the intact and jointed rock mass models which are printed by laser rapid prototyping printer with photosensitive resin materials, stress-strain curve and fracture propagation are obtained, and the mechanical properties of 3D printed rock mass are studied. The results show that the intact model of the photosensitive resin material has greater plasticity and stress hardening after the peak strength, while the jointed models have obvious brittle mechanical characteristics, but in general, plastic deformation occurs before brittle failure; that the joint dip angle has an important influence on the physical parameters such as the peak strength of the model, strain at brittle fracture, elastic modulus, and the crack propagation; and that photosensitive resin material can simulate rock fracture, but it is not as good as natural rock or rock-like material. The research results can be used for reference in the study of mechanical properties of photosensitive resin and its application in 3D printing for rock mass.

Experimental study of blasting wave propagation in jointed rock mass and vibration reduction effect of barrier holes

Blasting in underground rock opening could generate shock waves, propagating in surrounding rock mass and possibly leading to damage and instability of surrounding underground structures. Barrier holes are widely used in blasting vibration reduction. However, characteristics of blasting wave propagation in jointed rock masses have not been well determined, and the understanding of effect of barrier holes on vibration reduction is still at its infancy. To investigate the blast-induced wave propagation in jointed rock masses and vibration reduction effect of barrier holes, laboratory explosion tests were performed with the super dynamic strain test system and vibration monitor system. Results showed that the joint orientation has significant effects on the first-peak compressive strains in surrounding rock mass and adjacent opening. First-peak compressive strain of surrounding rock mass increases with decreasing scaled distance. The first-peak compressive strain on the wall of the adjacent underground opening is dependent on the characteristics of the adjacent underground opening. In addition, the dynamic responses of the surrounding rock mass are determined by the combined influence of the joint dip angle and location. The experimental results also indicated that barrier hole diameter has great effects on first-peak compressive strains of adjacent underground opening and the vibration-isolation rate of measuring points before and after barrier hole screen. With increasing barrier hole diameter, first-peak compressive strains and peak particle velocities (PPVs) significantly decrease and vibration-isolation rate of measuring points before and after barrier hole screen increases, indicating the vibration reduction effect of barrier hole increases. The findings in this paper could facilitate better understanding blasting wave propagation in jointed rock mass, and be helpful in vibration control of engineering explosions.